Er. Revati Raman

Diversion tunnels are the lifelines of hydroelectric projects, ensuring safe river passage and dry working conditions during dam construction. However, when they fail, the consequences can be severe: flooding of construction site, derailed timelines, inflated costs, and significant safety risks. In many projects in the Himalayan Region, tunnel blockages and collapses due to landslides and weak geology have led to major schedule disruptions and even near-catastrophic events. In the Himalayas, tunnel instability remains a challenge, with shear zones, high in-situ stresses, fractured rock masses, and unpredictable floods continually testing the limits of design and construction. The message is clear: diversion tunnels may be temporary structures, but they demand permanent engineering rigor in design, construction, and monitoring.

Spillways of Himalayan dams are subjected to some of the most severe hydraulic conditions. During monsoon, rivers like the Sutlej carry enormous boulders sometimes exceeding 5 metres in diameter along with heavy sediment loads that cause extreme abrasion and erosion of concrete surfaces. In collaboration with IIT Delhi, the design team developed High-Performance Concrete (HPC) and High-Performance Fiber Reinforced Concrete (HPFRC) incorporating silica fume, fly ash, and micro steel fibers, engineered specifically for high abrasion resistance and durability. These materials have shown remarkable resistance to abrasion, promising to significantly reduce annual repair frequency and enhance long-term durability of structures. Engineering in the Himalayas is not just about strength — it's about resilience, innovation, and foresight.

Glacial Lake Outburst Floods (GLOFs) are no longer rare events but an emerging design and operational reality in the Himalayan region, driven by accelerated glacier retreat and rapid expansion of unstable moraine-dammed lakes. Sudden breach can release enormous volumes of water, debris, and sediment within a short time, causing severe damage to downstream rivers, bridges, roads, and hydropower infrastructure. Addressing GLOF risk requires a shift from historical hydrology to climate-informed hazard assessment, basin-level planning, resilient engineering practices, remote sensing, early warning systems, and clear dam operation protocols. For Himalayan infrastructure, integrating GLOF risk into planning, design, and operation is no longer optional — it is essential. The Central Water Commission (CWC) has issued Guidelines for Structural Measures to Mitigate Adverse Effects of GLOF on Dams (July 2025), which must be strictly followed.

Designing a barrage on Himalayan bouldery rivers requires special attention to seepage and foundation behavior due to highly pervious, widely graded riverbed material and extreme flow conditions. One of the most critical yet often overlooked risks is suffusion — where finer particles migrate through the voids of a coarse boulder matrix under seepage forces, leading to internal erosion and long-term instability. Suffusion develops silently and can compromise the safety of the structure if not properly addressed. Barrage design must go beyond conventional alluvial assumptions and include armoring-based scour assessment, exit gradient and seepage analysis using numerical methods, explicit suffusion risk evaluation, and appropriate provision of cut-offs and impervious floors. IS 6966 (Part 2) for gravelly and bouldery river reaches is hoped to be released soon by BIS.

Rock Filled Concrete (RFC) has emerged as an innovative and sustainable alternative to conventional mass concrete for large hydraulic and civil engineering structures such as dams. In RFC, large sound boulders are pre-laid within the formwork, and a highly flowable self-compacting concrete (HSCC) fills the voids without any need for vibration or roller compaction, creating a dense, monolithic structure with excellent strength, durability, and crack resistance. The use of rocks significantly reduces cement consumption, lowers the heat of hydration, minimises thermal cracking risk, and the rocks act as natural crack arrestors. China has successfully constructed many large dams using RFC. Given India's upcoming large hydropower projects and PSPs, RFC should be actively explored — offering cost savings, faster execution, and improved environmental sustainability. RFC is more than just an alternative material; it represents a sustainable shift in dam engineering.